The present invention relates to a process and apparatus for bonding metal wire to a substrate and more particularly a process for bonding lead wires to lead frames by electrodepositing a spot of metal over a portion of the lead wire and substrate.
Presently, in the field of microelectronics, lead wires are bonded to lead frames by either a thermocompression procedure or an ultrasonic bonding technique. A typical process and apparatus for thermocompression bonding metallic elements is disclosed in U.S. Pat. No. 3,263,057. The metallic wire and substrate are positioned on a support member, and a predetermined pressure is applied to the location where the joint or bond is desired. At the same time, a predetermined amount of heat is applied to the joint area by means of an applied current so as to achieve a diffusion bond at the compression diffusion joint area. While the thermocompression bonding technique is widely employed in the field of microelectronics, it suffers from a number of disadvantages. The metal substrate to which the wire is to be bonded is generally gold plated in order to assure a strong bond and good electrical contact. The plating requirement makes the thermocompression technique extremely expensive to practice. In addition, when working with certain delicate transistors, the temperatures required to effect the thermocompression bond (temperatures as high as 400.degree. C.) have a detrimental effect on the transistor.
A typical ultrasonic bonding method and apparatus is disclosed in U.S. Pat. No. 4,037,772. In this case a bonding head is wobbled so that a contact point on the bonding head progressively moves along the lead wire and substrate interface and acts thereion to firmly bond the lead wire in good electrical contact with the metal substrate. This particular technique has not been widely accepted in the industry due to the expensive setup costs and expensive machinery required to practice the technique.
Clearly, it would be of considerable advantage and highly desirable to effectively bond the lead wires to a substrate without incurring the high costs associated with the known techniques.
Accordingly, it is the principal object of the present invention to provide a process and apparatus for bonding a lead wire to a metal substrate by electrodepositing a spot of metal over a portion of the lead wire and substrate.
It is a particular object of the present invention to provide a process and apparatus as above which is relatively inexpensive when compared to known approaches.
Further objects and advantages of the present invention will appear hereinbelow.